It is known to dry or treat materials by depositing such wet material upon a foraminous conveyor or perforate support and advancing the material along while blowing heated air through it, the air being returned to heating (or cooling) and/or drying means and recirculated. Such treatment is used for toasting, puffing, cooling, curing, conditioning, or treatment involving chemical or physical reactions on a product.
Prior U.S. Pat. No. 3,214,844, to F. B. Oates et al, discloses one such apparatus comprising a conveying means in the form of a plurality of connected open top receptacles, each having a perforate bottom. The conveying means are positioned within a treatment chamber, and means are provided for passing a treating gas upwardly through the perforate bottoms of the open top receptacles to fluidize or levitate particulate material disposed within the receptacles. Movement of the conveying means longitudinally within the treating chamber causes the particles within the open top receptacles to be conveyed longitudinally through the chamber. An alternative embodiment disclosed in this patent comprises a screw conveyor positioned within a longitudinally extending trough having a perforate bottom, the screw conveyor advancing fluidized material in said trough longitudinally along the trough. Several problems exist with regard to the apparatus of this patent. For one, such apparatus is cumbersome in structure and bulky, making it extremely expensive to manufacture. In addition, particularly in the embodiment employing a plurality of successive, connected receptacles, it is a problem to seal the areas between the receptacles against either lodging of material in such areas or bypassing of the receptacles by the treating gas.
An improved apparatus is disclosed in prior U.S. Pat. No. 3,293,768, to Blank and Scott, comprising a traveling perforate bottom support for material to be treated, means for forcing gas upwardly through the support in a series of longitudinally spaced parallel streams along the length of travel of the support to lift and fluidize the material in each upwardly flowing stream of gas, and additional means returning at least part of the gas down through the bed of material in a plurality of down-flowing streams intermediate the up-flowing streams to redeposit material on the bed, establishing a kind of rolling or tumbling of the fluidized material within the bed.
The '768 patent is assigned to assignees of the present application, and the disclosure of such patent is incorporated by reference herein.